Short-wavelength, high-amplitude gravity anomalies around the Banda Sea, and the collapse of the Sulawesi orogen

In eastern Indonesia, high-density ophiolitic rocks outcropping on islands surrounding the Banda Sea are in many cases associated with strong gravity anomalies and steep gravity gradients. However, the relationships are not a lways straightforward. Bouguer gravity levels and gradients over the extens ive East Sulawesi Ophiolite are generally relatively low, although short wa velength, high amplitude anomalies indicate rapid changes in thickness of h igh-density rocks in a few places. In the Banda Are. most local positive an omalies due to ophiolites are superimposed on a steep regional gravity grad ient but in one case, in western Seram, there is a distinct and important s patial separation between the two. On Buru, west of Seram, a gradient of mo re than 10 mGal/km testifies to the presence of very dense rocks in the nea r subsurface, despite the absence of ophiolites in the outcrop. Gravity variations and ophiolite distribution around the Banda Sea are comp atible with extension having occurred in the Sulawesi region following, and as a result of, Oligo-Miocene collision with an Australian-derived microco ntinent. Similar histories have been proposed for many Mediterranean deep b asins of similar size, shape and character, and emplacement of some of the high-density masses in the Banda Are has probably resembled at least the la ter stages in the emplacement of peridotite massifs in the Rif-Betic belt. In both areas the present close association of the ultramafic rocks and the ir associated local anomalies with a strong regional gravity gradient is la rgely coincidental. (C) 2001 Elsevier Science B.V. All rights reserved.